Getter-sputtering apparatus

ABSTRACT

Apparatus and method for getter-sputtering. Material is sputtered from a cathode onto a substrate at a low pressure in an inert atmosphere. Sputtering is effected in a sputter space to which there is access of gas only by way of a gettering antechamber while sputtering is taking place. The sputter space may be arranged co-axially within the gettering space either in a planar arrangement or an arrangement of co-axial chamber with a dividing wall. Alternatively, the gettering chamber may be arranged above the sputter chamber.

Sept 12, 1972 w, JAMES ET AL 3,691,053

GETTER-SPUTTERING APPARATUS 2 Sheets-Sheet 1 Filed Dec. 29, 1969 DAVIDWILLIAM FRANCIS JAMES, DAVID OWEN SPILLER and HARVEY DAVID COLTMAN,

Attorneys p 7 D. w. F. JAMES ETAL 3,691,053

GETTER-SPUTTERING APPARATUS Filed Dec. 29, 1969 2 Sheets-Sheet 2 GC E MDW U l/o DAVID WILLIAM FRANCIS JAMES, DAVID OWEN SPILLER and HARVEYDAVID COLTMAN, Inventors Attorneys United States Patent @fice 3,691,053GETTER-SPUTTERING APPARATUS David W. F. James, David O. Spiller, andHarvey D.

Coltman, Bangor, Wales, assignors to University College of North Wales,Bangor, Wales Filed Dec. 29, 1969, Ser. No. 888,493 Claims priority,application Great Britain, Jan. 2, 1969, 380/69; Nov. 20, 1969, 56,959/69 Int. Cl. C23c 15/00 US. Cl. 204-298 7 Claims ABSTRACT OF THEDISCLOSURE The invention relates to getter-sputtering apparatus and amethod of sputtering by establishing a clean atmosphere of inert gas bygetter action and depositing material onto a substrate by sputtering.The invention seeks to provide a method andmeans for depositing thinfilms of conductors and/or insulators for thin film and integratedcircuits and the like in materials hitherto difficult to use or inpurities hitherto difiicult to obtain because of low sputtering rates orother poor characteristics.

According to one aspect of the invention there is providedgetter-sputtering apparatus having a housing within which is a sputterspace; means for mounting in the sputter space a substrate on whichmaterial is to be sputtered; a sputter cathode in the sputter space; agetter space in the housing, access of gas to the sputter space being byway of the getter space only; and a getter electrode in the getterspace.

In one embodiment of the invention the sputter space and getter spaceare chambers within the housing, which chambers are divided by adividing wall around which is the only access for gas to the sputterchamber. The sputter chamber may be cylindrical and the getter chambermay be an annular chamber surrounding the sputter chamber, the substratebeing supported on a platform which is brought up against the rim of thecylindrical dividing wall.

Alternatively the housing may comprise an open-topped can with aremovable lid and a removable transverse partition constituting thedividing wall, the sputter chamber being the space below the partitionand the getter chamber being the space above the partition.

In another embodiment of the invention the sputter space and the getterspace are defined between a planar cathode assembly and a parallel flatanode surface spaced a short distance therefrom, the planar cathodeassembly comprising a shield having a flat face on or near which aremounted sputter and getter cathodes parallel with the face, the gettercathode being annular and surrounding the sputter cathode from which itis spaced. The shield is preferably an earthed metal shield and thegetter and sputter cathodes are accommodated in recesses in the flatface thereof.

The getter and sputter cathodes may be energised from a direct currentsource, the cathodes being held negative with respect to the housing andthe substrate, which are 3,691,053 Patented Sept. 12, 1972 earthed, forexample. Getter action in the getter space is then effected by dischargebetween the getter electrode (cathode) and the wall of the housing orthe anode surface. Alternatively, the getter and sputter cathodes may beenergised by radiofrequency currents. This is particularly suitable forthe deposition of insulators.

According to another aspect of the invention there is provided a methodof sputtering material onto a substrate comprising the steps ofsupporting the substrate in a sputter space to which gas may enter onlyby way of a getter space, introducing an inert atmosphere atsub-atmospheric pressure into the sputter and getter spaces, getteringthe gas in the spaces and sputtering material into the substrate from asputter cathode while maintaining gettering action in the getter space.

The inert gas may be argon maintained at a pressure of about 10- torr.The argon may be pre-purified, if required, before being passed to theenclosure by passage over manganous oxide, thus removing oxygen, whichis the major impurity.

The invention will further be described with reference to theaccompanying drawings, of which:

FIG. 1 is a perspective view, broken away in part, of apparatusaccording to the invention;

FIG. 2 is a sectional elevation of a modified form of the apparatus ofFIG. 1; and

FIG. 3 is a sectional elevation of further apparatus in accordance withthe invention.

Referring to FIG. 1, the apparatus comprises a stainless steel canhaving a cylindrical body H with a fixed base I. The can has a removablelid A carrying three rods B to which is fixed a platform C which is asliding fit in the can. The platform divides the can into a lower,sputtering chamber S and an upper, getter chamber T. Within the getterchamber is an annular getter cathode D of copper which is supported on ahigh quality ceramic lead-through insulator G so as to define an annulargap with the body of the can. The gap lies beneath the rim of the can.The body of the can is earthed and constitutes the getter anode.

The sputtering chamber includes a sputtering cathode E mounted at theend of a high quality lead-through insulator F fixed to the lid A andthe platform C. The substrate to be sputtered is mounted on a support Kwhich includes a heater which is energised by leads passing throughleadthrough I. A shutter M is controllable manually from outside the canso as to obscure a determined part of the substrate. The shutter isoperated via a vacuum seal on a click-stop mechanism. This enables thewhole substrate to be uncovered or various parts to be uncovered insequence thereby making deposition of thin film thermocouples possible.

In a typical sputtering operation in accordance with the invention thefollowing procedure is adopted. Firstly the substrate on which thesputtered film is to be deposited is mounted on support K. Lid A andplatform C are then replaced, together with cathodes D and E. The can ismounted in an enclosure (not shown) which may be a vacuum collararrangement as shown at VC in FIG. 2 (to be described more fully). Theenclosure is evacuated to a pressure of 10- torr and back filled withargon several times. A flow of 99.995 argon at about 10- torr is thenmaintained in the enclosure.

A gettering discharge is then established in the getter chamber atapproximately 1.2 kv. and 10 ma. for 30 minutes. The sputtering cathodeis then caused to sputter for some time to getter the inner section ofthe can and also remove surface impurities from the sputtering cathodebefore opening the shutter M and allowing film deposition to take place.Conditions vary with the material of the sputtering electrode but formolybdenum typical conditions would be approximately 2.3 kv. for 30minutes at 6 ma. followed by film deposition.

A thermocouple (not shown) is mounted on support K to monitor thetemperature of the substrate and thermocouple leads therefor areconnected to monitoring equipment through sealed lead-in connections L.

Comparative tests have been carried out on a number of materialsproducing films both with and without the use of the annular getteringelectrode D. Film resistance has been used as a criterion for evaluatingany apparent improvement in film quality resulting from the use of theextra gettering electrode. In almost every case there was a mostnoticeable improvement in film quality. Even in the case of copper,which itself sputters rather quickly, an improvement was obtained. Inthis case a slight difference in colour in the deposited films was alsoapparent when the extra electrode was brought into use. The followingresults indicate the improvement obtained in the case of copper andmolybdenum films; the ratio of film resistance without the getterelectrode operating to that with the getter electrode operating is, forthe case of copper, 12:1 and for molybdenum, 3.5: 1.

Referring now to FIG. 2, there is shown apparatus basically the same asin FIG. 1 but having a sliding support SS for the substrate which allowsthe substrate to be changed by removal through the wall of the can.There is a gas seal GS in the wall of the can where support SS enters.

FIG. 2 shows a vacuum collar VC surrounding the can, means (not shown)being provided for pumping out the space within the collar by way of avacuum outlet V and filling it with argon by way of an argon inlet AI. Afiat top is sealed over the collar and supports a radio-frequencymatching unit MU which supplies R.F. signals to the getter and sputterelectrodes.

Referring now to FIG. 3, there is shown another form of thegetter-sputtering apparatus. There is a sputtering chamber S defined bya cylindrical dividing wall DW open at the bottom and sealed at the topto the top of a cylindrical casing CC. The substrate SU is supported ona platform P which is brought up against the rim of wall DW so thatthere is at most only a small space therebetween. The annular chamber GCsurrounding the Wall DW is the getter chamber and includes an annulargetter cathode D.

The casing CC is strong enough to withstand atmospheric pressure whenexhausted and the space within it is pumped out directly, there being noneed for an additional vacuum chamber to include the apparatus as inFIGS. 1 and 2.

The walls of the casing, the getter and sputter electrodes and theplatform P are all hollow and are provided with water cooling inlets andoutlets. This cooling is eifective to inhibit out-gassing from the metalsurfaces.

The invention is not restricted to the details of the above describedembodiments. For example, other materials such as certain compoundsemi-conductors may be sputtered. The film deposited may be amorphous,polycrystalline or a single crystal. Other inert gases than argon may beused. The operating gas pressure may be, for example, in the range 0.1to 100 microns.

What is claimed is:

1. A getter-sputtering apparatus comprising a housing in the form of acan with a lid, a transverse partition in said can forming a dividingwall dividing the can into a sputter chamber on the side of the wallremote from the lid and a getter chamber on the other side of the wall,the peripheral edge of the dividing wall being spaced from the can todefine a passage for gas to pass from the getter chamber to the sputterchamber, whereby access for gas to the sputter chamber is only by way ofthe getter chamber and said passage past said dividing wall, means formounting in the sputter chamber a substrate on which material is to besputtered, a sputter cathode in said sputter chamber, a getter cathodein said getter chamber, a gas inlet in said getter chamber and a gasoutlet from said sputter chamber.

2. An apparatus as claimed in claim 1 in which said housing is acylindrical can and the lid is a removable lid and said transversepartition is removably mounted in said housing.

3. An apparatus as claimed in claim 2 in which the partition, the getterelectrode and the sputter cathode are fixed to said lid and areremovable therewith.

4. An apparatus as claimed in claim 1 in which said housing is acylindrical can which is sufficiently strong to withstand atmosphericpressure when the inside is evacuated.

5. An apparatus as claimed in claim 1 in which said substrate mountingmeans comprises a slide support, the can having an aperture in the sidethereof through which said support is inserted and removed, and agas-tight seal between the support and the aperture.

6. Getter-sputtering apparatus having a housing within which is asputter chamber; a sputter cathode in the sputter chamber; a platformfor mounting in the sputter chamber a substrate on which material is tobe sputtered; an annular getter chamber in the housing, the getterchamber surrounding the sputter chamber; a getter cathode in the getterchamber; a gas inlet in said getter chamber and a gas outlet from saidapparatus; and a dividing wall dividing the sputter chamber from thegetter chamber, the dividing wall having a rim extending close to saidplatform for defining with said platform a passage for the gas to passto the sputter chamber, which passage is narrow with respect to thecross-sectional areas of the chambers, whereby access for gas to thesputter chamber is only by way of the getter chamber and past thedividing wall.

7. Apparatus as claimed in claim 6 wherein the housing has a cylindricalcasing which defines the getter chamber and which encloses the platform,the casing being sufficiently strong to withstand atmospheric pressurewhen the inside is evacuated.

OTHER REFERENCES Seeman: Bias Sputtering: Its Techniques andApplication, Vacuum, p. 133 (1966).

HOWARD S. WILLIAMS, Primary Examiner S. S. KANTER, Assistant ExaminerU.S. C1. X.R. 204192

